## Summary
Part of #17412
Starred expressions cannot be used as values in assignment expressions.
Add a new semantic syntax error to catch such instances.
Note that we already have
`ParseErrorType::InvalidStarredExpressionUsage` to catch some starred
expression errors during parsing, but that does not cover top level
assignment expressions.
## Test Plan
- Added new inline tests for the new rule
- Found some examples marked as "valid" in existing tests (`_ = *data`),
which are not really valid (per this new rule) and updated them
- There was an existing inline test - `assign_stmt_invalid_value_expr`
which had instances of `*` expression which would be deemed invalid by
this new rule. Converted these to tuples, so that they do not trigger
this new rule.
Summary
--
Detects starred assignment targets outside of tuples and lists like `*a
= (1,)`.
This PR only considers assignment statements. I also checked annotated
assigment statements, but these give a separate error that we already
catch, so I think they're okay not to consider:
```pycon
>>> *a: list[int] = []
File "<python-input-72>", line 1
*a: list[int] = []
^
SyntaxError: invalid syntax
```
Fixes#13759
Test Plan
--
New inline tests, plus a new `SemanticSyntaxError` for an existing
parser test. I also removed a now-invalid case from an otherwise-valid
test fixture.
The new semantic error leads to two errors for the case below:
```python
*foo() = 42
```
but this matches [pyright] too.
[pyright]: https://pyright-play.net/?code=FQMw9mAUCUAEC8sAsAmAUEA
(Supersedes #9152, authored by @LaBatata101)
## Summary
This PR replaces the current parser generated from LALRPOP to a
hand-written recursive descent parser.
It also updates the grammar for [PEP
646](https://peps.python.org/pep-0646/) so that the parser outputs the
correct AST. For example, in `data[*x]`, the index expression is now a
tuple with a single starred expression instead of just a starred
expression.
Beyond the performance improvements, the parser is also error resilient
and can provide better error messages. The behavior as seen by any
downstream tools isn't changed. That is, the linter and formatter can
still assume that the parser will _stop_ at the first syntax error. This
will be updated in the following months.
For more details about the change here, refer to the PR corresponding to
the individual commits and the release blog post.
## Test Plan
Write _lots_ and _lots_ of tests for both valid and invalid syntax and
verify the output.
## Acknowledgements
- @MichaReiser for reviewing 100+ parser PRs and continuously providing
guidance throughout the project
- @LaBatata101 for initiating the transition to a hand-written parser in
#9152
- @addisoncrump for implementing the fuzzer which helped
[catch](https://github.com/astral-sh/ruff/pull/10903)
[a](https://github.com/astral-sh/ruff/pull/10910)
[lot](https://github.com/astral-sh/ruff/pull/10966)
[of](https://github.com/astral-sh/ruff/pull/10896)
[bugs](https://github.com/astral-sh/ruff/pull/10877)
---------
Co-authored-by: Victor Hugo Gomes <labatata101@linuxmail.org>
Co-authored-by: Micha Reiser <micha@reiser.io>
